In a standard vehicle drive system it is well known to provide a torque converter between the crankshaft of an internal combustion engine and a transmission to control torque so as to smooth drive speed changes in response to operator selected drive modes made by manual or electrical setting of gear shift consoles operatively coupled to a multi-speed transmission. Examples of such prior art torque converters are shown in U.S. Pat. Nos. 3,497,043; 4,951,788 and 5,129,493. Typically, such torque converters include a lock-up clutch to produce a direct drive connection between the engine and the transmission. Furthermore, such torque converters include a damper assembly to absorb torque fluctuations from the input drive once the impeller and turbine of the torque converter are interconnected by known torque lock-up clutches.
U.S. Pat. No. 5,789,823 has an engine and/or the electric motor operated to power the vehicle. In order to provide for a desired control of power, a one-way clutch is connected between a lock-up clutch and a start clutch. The arrangement is operative to provide a high torque input from the electric motor through the torque converter turbine to the engine. Once the engine starts, the start clutch is disengaged and the engine drive is directly connected through the one-way clutch that is operative to lock in the direct drive direction so as to power the torque converter impeller or pump. Once full power is transmitted through the torque converter to the transmission, the lock-up clutch is operated to produce a 1:1 drive to the transmission in bypassing relation with the torque converter. In this configuration the one-way clutch is locked up in the drive direction during initial torque converter operation and is operative to free wheel in the drive direction when the electric drive rotor is rotating faster than the engine speed so as to permit overrunning or free-wheeling between the engine and the rotor of an electric motor. Hence, the location of the one-way clutch and its operation is predicated upon an arrangement in which the stator of the electric motor is directly connected to the input housing of the torque converter for propelling the vehicle during various modes of highway operation. There is no provision for lock-up during vehicle coasting or during regenerative braking.
While suitable for its intended purpose the arrangement of the one-way clutch in the torque converter of the '823 patent does not provide for a continuous free-wheel connection between the engine and the impeller or pump of a torque converter in the drive direction and it is not operative to lock upon overdrive from the transmission to the engine during vehicle coasting.
One example operating characteristic of certain prior art torque converters including the combination shown in the '823 patent is that in operating modes in which the transmission selector is in a forward drive and the accelerator and brake are operated such that the vehicle is coasting down in speed and fuel flow to the engine is reduced to idle speed requirements, the engine can stall or its speed can fall off or droop. In such cases the vehicle driver may feel the pull of the engine when it is restarted in the case of stall or when it is operated to pull back from the drooped speed to the coasting speed of the vehicle as manifested by the vehicle wheels back driving the transmission through the output shaft of the vehicle drive system. Furthermore, advantages of regenerative braking and charging of a battery pack are lost if the engine must be restarted.